I dont know if this has ever been mentioned before, but any way here goes :-
You know the little white bags of silica gel (do not eat throw away) you get in some electrical goods, kids toys etc, well, I all ways keep a couple in my rifle sleeve, reason being they attract moisture like s**t and keep things dry. You know the story your out in the field and even if its not raining cold steel attracts moisture, you get home and clean etc, but you will never remove all the moisture.
So to keep your rifle in tip top and avoid moisture just place a couple of these little silica gell bags in